The present invention relates generally to chemical and biochemical analysis, and more particularly, to systems and methods for performing chemical and biochemical analyses of a sample within a microfluidic device.
Analysis of chemical and biochemical samples often requires detection and identification of the constituent elements of the sample. Microfluidic devices are often used to separate and control movement of the elements of the sample to detect a property of the elements with a detection system. The microfluidic devices typically include multiple wells that are interconnected with microchannels for transport of the sample. Application of a voltage across the channels permits the electrophoretic migration of macromolecular species in the sample. The samples often include an intercalating dye that becomes more fluorescent upon binding to the species of the sample. The fluorescent dyes are used to identify and locate a variety of cell structures such as specific chromosomes within a DNA sequence.
A variety of devices have been designed to read fluorescent labeled samples. In general the devices include at least one light source emitting light at one or more excitation wavelengths and a detector for detecting one or more fluorescent wavelengths. The light source is often a laser that emits light at one narrow center wavelength (single mode laser). For example, the laser may be optimized to operate at a single wavelength of 640 nm at full power, as shown in FIG. 1. However, as the temperature of the drive current of the laser changes, the wavelength typically changes. For example, when the laser is first turned on, the operating wavelength of the laser will increase as the laser wanns up. If these wavelength changes were to occur as smooth transitions, the effect on the system could be minimized by warming up the laser prior to use or correcting the output of the laser to compensate for a slow wavelength drift.
Instead of smooth transition, the wavelength changes due to variations in temperature and drive current occur at sharp transitions or steps, as shown in FIG. 2. These abrupt wavelength changes are often referred to as laser mode hops and may result in spikes in the output data, because the optical detection system will behave differently at different emission wavelengths, due to the optical components, the reference detector, the chemical sample and the light source that often have slightly different attenuation or coupling at different wavelengths. This can lead to misidentification of the samples. The laser mode hops may even occur after a laser has warmed up if the system stabilizes at a temperature near a mode hop where slight variations in temperature will cause a sharp change in wavelength. Furthermore, the laser mode hops may affect detection system components which have characteristics dependent on the laser wavelength. The laser mode hops are difficult to correct for and may cause detection errors, particularly in electrophoresis, DNA sequencing, or cell analysis which requires detection of small changes in signals.
There is, therefore, a need for techniques that reduce sudden changes in the emitted light source wavelength due to temperature variations in the light source.
The present invention provides methods and systems for analyzing samples. One method of the present invention generally includes positioning the sample within an optical path of a light source and providing power to the light source. The light source power is modulated such that light is emitted from the light source in more than one mode to reduce changes in the emitted light due to temperature changes in the light source. The method can also include detecting the intensity of light emitted from the sample upon exposure to the light source.
In one embodiment of the present invention, the system generally includes a light source operable to transmit light onto the sample and a detector operable to detect intensity of the light emitted from the sample. The system further includes a power modulator operable to modulate the light source power such that light is emitted from the light source in more than one mode to reduce changes in the emitted light due to temperature changes in the light source.
In another embodiment, the system includes a microfluidic device for holding the sample and positioning the sample in an optical path of the light source.
The above is a brief description of some features and advantages of the present invention. Other features, advantages, and embodiments of the invention will be apparent to those skilled in the art from the following description, drawings, and claims.